Greetings from syncfusion support,
We are currently investigating your query regarding the issue with the available space in the Grid not being used effectively to display records when using grouping.
By default, the Grid will render 12 records when the height property is set, and you cannot define the page size property. When grouping in a Grid based on a column, it should include the space by default. You cannot render the next page records on the current page and move the records when you expand the Grid rows.
Based on the provided code, we suggest setting the 'height' property to 'auto' or removing it altogether. This will allow the Grid to adjust its height dynamically, helping you to resolve the space problem.
Please feel free to reach out if you need further assistance.
Regards,
Sivaranjani.